It is desirable to provide for the removability of a rigid or hard disk drive from a computer system by the computer user. There is also a need for such disk drives to be of a reduced size, weight, increased information storage capacity, and dimensioned according to a predetermined industry standard or "form factor," and yet be of a lower cost to be competitive with drives using disposable recording media such as floppy diskettes, disk cartridges, and magnetic tapes.
Drives using removable storage media, such as floppies, cartridges, and tapes are frequently used by computer user for: interchanging information between computer systems; preserving security in the information; and long term archiving. Although removable media are relatively inexpensive, they are subject to certain disadvantages.
Drives using removable storage media generally give reduced performance, capacity, and reliability when compared with rigid or hard disk drives. As form factors have been dramatically reduced, the mass and size of key components in rigid disk drives have likewise been reduced. Such reduction in size has allowed the concept of removable rigid disk storage to be redressed. Accordingly, the manufactures of computer systems and disk drives have provided for rigid disks which are removable from the computer system in which they are used.
According to the prior art, there are three types of rigid removable disk devices available, excluding traditional floppies and tape. These include: rigid disks encased within a removable cartridge, plug compatible external disk drives configured as "side-cars", and rigid disk drives removable from a specially adapted external mounting frame installed in a disk bay of a computer.
With respect to rigid disk cartridges, as with any separately removable media, head positioning and alignment errors become very significant and ultimately limiting factors to storage density or capacity. Also the registration of disk to spindle after cartridge insertion adds additional error and also limits the areal density. Both factors also directly effect performance and cost. To ensure reliability of the media in the cartridge, complex purge and seal systems are required to prevent media and head failure caused by contaminants introduced during removal and reinsertion of the cartridge in the drive. For all of these reasons, known disk cartridges do not present an ideal removable rigid disk storage device for the computer user.
External rigid disk drives or side-car drives may be considered a removable storage device, since the drive can easily be unplugged from the computer by the user. The known external drives tend to be bulky, and of necessity require cabling and compatible plugs on both the computer and the cable which decrease reliability. Furthermore, side-car drives present an awkward balancing problem to the laptop or notebook computer user, and are only negligibly amenable to pocket stuffing.
The various forms of removable media considered up to this point are often confused with true removable drives, that is a disk storage device where the total drive mechanism is removed from the host environment. To date, all of the known removable rigid or hard disk drives consist of traditional drive units packaged within an additional set of exterior mechanics, or mounting frames, to allow their removability. That is, the mounting frame generally increases the size of the overall unit. For example, a 31/2" disk drive is generally removably mounted in an exterior frame fitted into a 51/4" form factor disk bay in a computer. Likewise, known 21/2" drives, generally require external frames sized to fit in 31/2" disk bays.
Additional electrical interconnects are generally required at a reduction in overall reliability. The traditional drives contained in such units have not been specifically designed to operate within the portable environment, but are merely adapted to portability after the fact. As such, their ability to survive in such applications is dependent on a variety of factors. The additional packaging required adds costs, weight, complexity, and aggravates thermal problems.
The success of known exterior packaging varies greatly. While the packaged drives are much more rugged than their non-packaged versions, none offer the protection normally obtainable with price competitive removable media. In addition, the prerequisite exterior mounting frame increases the physical size of the unit to the extent that it is only marginally adaptable to the laptop, and generally entirely excluding the needs of the growing notebook-sized computer user.
There is consequently a significant need for a reduced size rigid disk drive which is self-contained, and removable from the host computer by a user.